Backside emitter solar cell structure having a heterojunction and method and device for producing the same

ABSTRACT

A backside emitter solar cell structure having a heterojunction, and a method and a device for producing the same. A backside intrinsic layer is first formed on the back side of the substrate, then a frontside intrinsic layer and a frontside doping layer are formed on the front side of the substrate, and finally a backside doping layer is formed on the back side of the substrate.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a method for producing a backsideemitter solar cell structure having a heterojunction, wherein

-   -   to form an absorber of the backside emitter solar cell        structure, a crystalline semiconductor substrate having a doping        of a first conductivity type is provided;    -   on a front side of the semiconductor substrate, at least one        frontside intrinsic layer is produced from an intrinsic,        amorphous semiconductor material;    -   on the at least one frontside intrinsic layer, at least one        frontside doping layer is produced from an amorphous        semiconductor material having a doping of the first conductivity        type that is higher than the doping of the semiconductor        substrate;    -   at least one backside intrinsic layer made of an intrinsic,        amorphous semiconductor material is produced on a back side of        the semiconductor substrate;    -   to form an emitter of the backside emitter solar cell structure        on the at least one backside intrinsic layer, at least one        backside doping layer is produced from an amorphous        semiconductor material having a doping of a second conductivity        type, which is opposite to the first conductivity type;    -   at least one electrically conductive, transparent frontside        conduction layer is produced on the at least one frontside        doping layer;    -   at least one electrically conductive, transparent backside        conduction layer is produced on the at least one backside doping        layer;    -   a frontside contact is produced on the at least one electrically        conductive, transparent frontside conduction layer; and    -   a backside contact is produced on the at least one electrically        conductive, transparent backside conduction layer.

The invention further relates to a backside emitter solar cell structurehaving a heterojunction, having

-   -   an absorber made of a crystalline semiconductor substrate having        a doping of a first conductivity type;    -   at least one frontside intrinsic layer formed on a front side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one backside intrinsic layer formed on a back side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one frontside doping layer formed on the at least one        frontside intrinsic layer made of an amorphous semiconductor        material having a doping of the first conductivity type that is        higher than the doping of the absorber;    -   an emitter of at least one backside doping layer formed on the        at least one backside intrinsic layer and made of an amorphous        semiconductor material having a doping of a second conductivity        type that is opposite to the first conductivity type;    -   at least one electrically conductive, transparent frontside        conduction layer formed on the at least one frontside doping        layer;    -   at least one electrically conductive, transparent backside        conduction layer formed on the at least one backside doping        layer;    -   a frontside contact formed on the at least one electrically        conductive, transparent frontside conduction layer, and    -   a backside contact formed on the at least one electrically        conductive, transparent backside conduction layer.

In addition, the invention relates to a device for producing a backsideemitter solar cell structure having a heterojunction, having

-   -   an absorber made of a crystalline semiconductor substrate having        a doping of a first conductivity type;    -   at least one frontside intrinsic layer formed on a front side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one backside intrinsic layer formed on a back side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one frontside doping layer formed on the at least one        frontside intrinsic layer made of an amorphous semiconductor        material having a doping of the first conductivity type that is        higher than the doping of the absorber;    -   an emitter of at least one backside doping layer formed on the        at least one backside intrinsic layer and made of an amorphous        semiconductor material having a doping of a second conductivity        type that is opposite to the first conductivity type;    -   at least one electrically conductive, transparent frontside        conduction layer formed on the at least one frontside doping        layer;    -   at least one electrically conductive, transparent backside        conduction layer formed on the at least one backside doping        layer;    -   a frontside contact formed on the at least one frontside        conduction layer; and    -   a backside contact formed on the at least one backside        conduction layer.

A method for producing a solar cell having a heterojunction and afrontside emitter is known from publication EP 2 682 990 A1. In theknown method, a layer stack consisting of a frontside amorphousintrinsic semiconductor layer and a frontside amorphous dopedsemiconductor layer is first deposited on a front side of asemiconductor substrate having a doping of a first conductivity type.The frontside amorphous doped semiconductor layer has a doping of asecond conductivity type, which is opposite to the first conductivitytype. A layer stack consisting of a backside amorphous intrinsicsemiconductor layer and a backside amorphous doped semiconductor layeris then deposited on the back side of the semiconductor substrate. Thebackside amorphous doped semiconductor layer has a doping of the sameconductivity type as the semiconductor substrate.

Then a transparent, electrically conductive layer is deposited on thefrontside as an anti-reflection layer without structuring and then anelectrically conductive backside coating is applied to the back side viaa mask, so that the electrically conductive backside coating is notdeposited on the layer stack formed on the substrate edge and thereforeno electrically conductive layer electrically contacts on the substrateedge. Finally, frontside and backside contacts are created.

This layer application sequence results in a layer sequence havingalternating doping on the edge of the substrate side, that is to say ann-p-n⁺ or a p-n-p⁺ sequence, each with an antireflection layer thereon.In the document EP 2 682 990 A1 it is pointed out that the layerdeposition sequence described must be adhered to in order to achieveadvantageous edge insulation in the solar cell to be formed. Inparticular, the frontside layer stack, which consists of the frontsideamorphous intrinsic semiconductor layer and the frontside amorphousdoped semiconductor layer, must be deposited in front of the backsidelayer stack, which consists of the backside amorphous intrinsicsemiconductor layer and the backside amorphous doped semiconductorlayer, in order to avoid the occurrence of shunt resistance on the solarcell edge.

To avoid undesirable solar cell edge shunts on a frontside emitter solarcell structure having a heterojunction, the document JP 2001044461 Afirst suggests the layer stack consisting of a backside amorphousintrinsic semiconductor layer and a backside amorphous dopedsemiconductor layer only in a region that is smaller than thesemiconductor substrate area at a distance from the substrate edge. Onlythen should the layer stack consisting of a frontside amorphousintrinsic semiconductor layer and a frontside amorphous dopedsemiconductor layer be deposited on the front side of the substrate.

A similar procedure is also described in US 2017/0207351 A1.

SUMMARY OF THE INVENTION

In contrast to the prior art mentioned above, the present invention isbased on a heterojunction solar cell structure having a backsideemitter. Such solar cells have the advantage over heterojunction solarcells having a frontside emitter that less stringent requirements mustbe placed on the optoelectric properties of the electrically conductive,transparent frontside conduction layer and on the design of thefrontside contact.

In the case of such backside emitter heterojunction solar cells, it iscustomary in the prior art to first deposit the intrinsic semiconductorlayer and the amorphous semiconductor layer doped having the sameconductivity type as the semiconductor substrate on the frontside of thesubstrate intended for incidence of light, and only then to form theintrinsic semiconductor layer and the amorphous semiconductor layerdoped differently than the semiconductor on the back side of thesubstrate.

However, it has been shown that the known shunt resistance and reversecurrent can assume considerable values in the known backside emitterheterojunction solar cells, and the solar cell characteristic suffersfrom this.

It is therefore the object of the present invention to improve theelectrical solar cell properties of backside emitter heterojunctionsolar cells.

This object is achieved on the one hand by a method for producing abackside emitter solar cell structure having a heterojunction, in which

-   -   to form an absorber of the backside emitter solar cell        structure, a crystalline semiconductor substrate having a doping        of a first conductivity type is provided;    -   on a front side of the semiconductor substrate, at least one        frontside intrinsic layer is produced from an intrinsic,        amorphous semiconductor material;    -   on the at least one frontside intrinsic layer, at least one        frontside doping layer is produced from an amorphous        semiconductor material having a doping of the first conductivity        type that is higher than the doping of the semiconductor        substrate;    -   at least one backside intrinsic layer made of an intrinsic,        amorphous semiconductor material is produced on a back side of        the semiconductor substrate;    -   to form an emitter of the backside emitter solar cell structure        on the at least one backside intrinsic layer, at least one        backside doping layer is produced from an amorphous        semiconductor material having a doping of a second conductivity        type, which is opposite to the first conductivity type;    -   at least one electrically conductive, transparent frontside        conduction layer is produced on the at least one frontside        doping layer;    -   at least one electrically conductive, transparent backside        conduction layer is produced on the at least one backside doping        layer;    -   a frontside contact is produced on the at least one electrically        conductive, transparent frontside conduction layer; and    -   a backside contact is generated on the at least one electrically        conductive, transparent backside conduction layer, wherein

the frontside and backside intrinsic layers and the frontside andbackside doping layers are produced in the following order:

-   -   Producing the at least one backside intrinsic layer on the        backside of the semiconductor substrate;    -   then producing the at least one frontside intrinsic layer on the        frontside of the semiconductor substrate;    -   then producing the at least one frontside doping layer on the at        least one frontside intrinsic layer; and    -   then producing the at least one backside doping layer on the at        least one backside intrinsic layer.

Surprisingly, this means that in the method according to the invention,first the intrinsic amorphous semiconductor layer on the backside of thesubstrate, that is to say the backside intrinsic layer, is produced,then the intrinsic amorphous semiconductor layer and the doped amorphoussemiconductor layer on the front side of the substrate and only then theamorphous semiconductor layer doped differently than the semiconductorsubstrate, that is to say the frontside doping layer on which the frontside of the substrate is produced, significantly improves the shuntresistance and the reverse current in all solar cells produced accordingto the invention. Thermographic measurements have also shown that theleakage current over substrate edges is greatly reduced by the sequenceof the method according to the invention. In addition, the quality ofthe passivation of the solar cells produced according to the inventionincreases, which is shown in a higher open circuit voltage and a betterfill factor of the backside emitter heterojunction solar cells. Inaddition, the solar cell efficiency is increased by the method accordingto the invention.

In a preferred variant of the method according to the invention, ann-doped semiconductor substrate is used as the semiconductor substrate,an amorphous semiconductor material doped with phosphorus is used toproduce the frontside doping layer, and an amorphous semiconductormaterial is used to produce the backside doping layer. Since borondiffuses faster than phosphorus and therefore spreads faster thanphosphorus in the system for producing the backside emitter solar cellstructure having heterojunction, the deposition of the boron-dopedbackside doping layer as the last layer has a particularly positiveeffect on the cleanliness of the system in the deposition of theamorphous layers.

In a preferred embodiment of the method according to the invention, thegeneration of the at least one frontside intrinsic layer on the frontside of the semiconductor substrate and the generation of the at leastone frontside doping layer on the at least one frontside intrinsic layerare carried out in processes which take place directly in succession inone and the same layer deposition reactor. As a result, only a singlelayer deposition reactor is required for the production of the frontsideintrinsic layer and the frontside doping layer, which overall simplifiesand makes the device for producing the backside emitter solar cellstructure having heterojunction more economical.

In addition, there is a particularly good edge insulation of thebackside emitter solar cell structure having heterojunction producedaccording to the invention if the at least one electrically conductive,transparent backside conduction layer is deposited on the at least onebackside doping layer at a distance from the side edge of thesemiconductor substrate, so that an edge region on the backside is notcoated with the electrically conductive, transparent backside conductionlayer and in all method steps for forming the electrically conductive,transparent backside conduction layer there is no electrical contactbetween the electrically conductive, transparent backside conductionlayer and the frontside conduction layer.

The object is further achieved by a backside emitter solar cellstructure having a heterojunction, having

-   -   an absorber made of a crystalline semiconductor substrate having        a doping of a first conductivity type;    -   at least one frontside intrinsic layer formed on a front side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one backside intrinsic layer formed on a back side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one frontside doping layer formed on the at least one        frontside intrinsic layer made of an amorphous semiconductor        material having a doping of the first conductivity type that is        higher than the doping of the absorber;    -   an emitter of at least one backside doping layer formed on the        at least one backside intrinsic layer and made of an amorphous        semiconductor material having a doping of a second conductivity        type that is opposite to the first conductivity type;    -   at least one electrically conductive, transparent frontside        conduction layer formed on the at least one frontside doping        layer;    -   at least one electrically conductive, transparent backside        conduction layer formed on the at least one backside doping        layer;    -   a frontside contact formed on the at least one electrically        conductive, transparent frontside conduction layer, and    -   a backside contact formed on the at least one electrically        conductive, transparent backside conduction layer, wherein

on one side edge of the backside emitter solar cell structure having theheterojunction on an edge region of the semiconductor substrate there isa layer sequence in the following sequence from the inside to theoutside:

-   -   the at least one backside intrinsic layer,    -   thereupon the at least one frontside intrinsic layer,    -   thereupon the at least one frontside doping layer and    -   thereupon the at least one backside doping layer.

Due to the layer structure on the side edge, i.e. the edge region of thebackside emitter solar cell structure, there is a significantimprovement in the shunt resistance and the reverse current of the solarcells produced according to the invention compared to backside emittersolar cell structures which have a conventional layer structure on theirside edge, in which the layers from inside out are in the followingorder or overlap in the following order:

-   -   the at least one frontside intrinsic layer,    -   thereon the at least one frontside doping layer,    -   then the at least one backside intrinsic layer, and    -   thereupon the at least one backside doping layer.

In a preferred embodiment of the backside emitter solar cell structurehaving heterojunction, the semiconductor substrate is an n-dopedsemiconductor substrate, the frontside doping layer is doped withphosphorus and the backside doping layer is doped with boron.

An advantageous embodiment of the backside emitter solar cell structurehaving heterojunction is constructed in such a way that the at least oneelectrically conductive, transparent backside conduction layer isdeposited on the at least one backside doping layer at a distance fromthe side edge of the semiconductor substrate, so that an edge region onthe back side is not coated with the electrically conductive,transparent backside conduction layer and there is no electrical contactbetween the electrically conductive, transparent backside conductionlayer and the frontside conduction layer.

The object is also achieved by a device for producing a backside emittersolar cell structure having a heterojunction, having

-   -   an absorber made of a crystalline semiconductor substrate having        a doping of a first conductivity type;    -   at least one frontside intrinsic layer formed on a front side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one backside intrinsic layer formed on a back side of        the absorber made of an intrinsic, amorphous semiconductor        material;    -   at least one frontside doping layer formed on the at least one        frontside intrinsic layer made of an amorphous semiconductor        material having a doping of the first conductivity type that is        higher than the doping of the absorber;    -   an emitter of at least one backside doping layer formed on the        at least one backside intrinsic layer and made of an amorphous        semiconductor material having a doping of a second conductivity        type that is opposite to the first conductivity type;    -   at least one electrically conductive, transparent frontside        conduction layer formed on the at least one frontside doping        layer;    -   at least one electrically conductive, transparent backside        conduction layer formed on the at least one backside doping        layer;    -   a frontside contact formed on the at least one frontside        conduction layer; and    -   a backside contact formed on the at least one backside        conduction layer, wherein

the device for producing the at least one frontside intrinsic layer onthe front side of the semiconductor substrate, the at least one backsideintrinsic layer on the back side of the semiconductor substrate, the atleast one frontside doping layer on the at least one frontside intrinsiclayer and the at least one backside doping layer on the at least onebackside intrinsic layer has only three layer deposition strands,wherein

-   -   a first layer deposition strand has at least one layer        deposition reactor for producing the at least one backside        intrinsic layer on the back side of the semiconductor substrate;    -   a second layer deposition strand has at least one layer        deposition reactor for producing the at least one frontside        intrinsic layer on the front side of the semiconductor substrate        and for producing the at least one frontside doping layer on the        at least one frontside intrinsic layer; and    -   a third layer deposition strand has at least one layer        deposition reactor for producing the at least one backside        doping layer on the at least one backside intrinsic layer;

and wherein at least one substrate transport and turning system isprovided between the first and second layer deposition strands andbetween the second and third layer deposition strands.

In contrast to the prior art, in the device according to the invention,the semiconductor substrate first passes through the first layerdeposition strand having the at least one layer deposition reactor forproducing the at least one backside intrinsic layer, is then turnedover, only after that the second layer deposition strand having the atleast one layer deposition reactor for producing the at least onefrontside intrinsic layer fed to the frontside of the semiconductorsubstrate and for producing the at least one frontside doping layer onthe at least one frontside intrinsic layer, then turned over again andonly finally transported into the third layer deposition strand havingthe at least one layer deposition reactor for producing the at least onebackside doping layer on the at least one backside intrinsic layer.

In a preferred embodiment of the device according to the invention, thefirst layer deposition strand has a backside intrinsic layer depositionreactor for producing the at least one backside intrinsic layer on theback side of the semiconductor substrate; the second layer depositionstrand has a single frontside layer deposition reactor for producing theat least one frontside intrinsic layer on the frontside of thesemiconductor substrate and the at least one frontside doping layer onthe at least one frontside intrinsic layer; and the third layerdeposition strand has a backside doping deposition reactor for producingthe at least one backside doping layer on the at least one backsideintrinsic layer; and the at least one substrate transport and turningsystem is provided upstream of the frontside layer deposition reactorbefore or in the second layer deposition strand.

Preferred embodiments of the present invention are explained in moredetail below with reference to figures, wherein

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 a to 1 i : schematically represent partial steps of a processsequence of an embodiment of the method according to the invention forproducing a backside emitter solar cell structure having heterojunctionusing cross-sectional views of the layer sequence generated in eachcase;

FIG. 2 schematically shows a layer stack formed on a side edge of anintermediate product of a backside emitter solar cell structure havingheterojunction according to the invention after the formation of theintrinsic and amorphous semiconductor layers;

FIG. 3 schematically shows a possible basic structure of a partialregion of a device according to the invention for producing backsideemitter solar cell structures having a heterojunction; and

FIG. 4 schematically shows a further possible basic structure of apartial region of the device according to the invention for producingbackside emitter solar cell structures having a heterojunction.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a to 1 i schematically show partial steps of a process sequenceof an embodiment of the method according to the invention for producinga backside emitter solar cell structure 1 having a heterojunction, as isshown schematically in cross-section, for example, in FIG. 1 i , usingcross-sections of each layer sequence produced. The layer thicknesses ofthe layers shown in the individual figures are not shown to scale.Although the ratio of the respective layer thicknesses to one another isalso not shown to scale, if one layer is shown thinner than another,this is typically also thinner in reality.

In the figures, the side of the respective layer structure shown aboveis the front side and the side shown below is the back side of therespective layer structure. The front side is the side into which lightis provided in the finished backside emitter solar cell structure 1.

FIG. 1 a schematically shows a crystalline semiconductor substrate 2, onthe front side and back side of which air oxide layers 21, 22 areformed. The semiconductor substrate 2 has a doping of a firstconductivity type. In the exemplary embodiment shown, the semiconductorsubstrate 2 is an n-doped silicon substrate, but in other embodiments ofthe invention can also be formed from another semiconductor materialand/or have a p-type doping. The n-doping is preferably a phosphorusdoping, but can also be formed with at least one other and/or at leastone additional dopant.

The air oxide layers 21, 22 in the example shown are SiO₂ layers havinga thickness between 0.2 and 3.0 nm.

The air oxide layers 21, 22 automatically form in the atmosphere on thepreviously cleaned semiconductor substrate 2. The semiconductorsubstrate 2 forms an absorber in the finished backside emitter solarcell structure 1.

FIG. 1 b shows the semiconductor substrate 2 from FIG. 1 a after afurther method step, in which the semiconductor substrate 2 is loadedinto a device for producing backside emitter solar cell structures 1having heterojunction. Portions of examples of such devices 30, 40 areshown in FIGS. 3 and 4 .

During charging, both sides of the semiconductor substrate 2 are exposedto the atmosphere at temperatures of typically below 200° C., so thatair oxide layers 23, 24, that is to say here SiO₂ layers having athickness of 0.2 to 3.0 nm, again form on the front side and the backside of the semiconductor substrate 2 or the air oxide layers 21, 22grow by the thickness of the air oxide layers 23, 24.

In a further process step of the method according to the invention,shown schematically in FIG. 1 c , at least one backside intrinsic layer3 made of an intrinsic, amorphous semiconductor material is deposited onthe back side of the semiconductor substrate 2 having the air oxidelayers 21, 22, 23, 24. The at least one backside intrinsic layer 3 ispreferably deposited using a PECVD method.

In the step shown in FIG. 1 d , by transporting and turning the layerstructure from FIG. 1 c to the next layer deposition reactor, air oxidelayers 25, 26 are in turn formed on the front side and back side of thelayer structure from FIG. 1 c . The air oxide layers 25, 26 in theexample shown are SiO₂ layers having a thickness of 0.2 to 3.0 nm. Theair oxide layer 25 grows directly on the air oxide layers 21, 23 thatalready exist on the front side. The air oxide layer 26 grows on thedeposited backside intrinsic layer 3.

After the backside intrinsic layer 3 has been deposited, at least onefrontside intrinsic layer 4 made of at least one amorphous intrinsicsemiconductor material and at least one frontside doping layer 5 made ofat least one amorphous semiconductor material having a doping of thefirst conductivity type which is higher than the doping of thesemiconductor substrate 2, are deposited on the front side of thesemiconductor substrate 2 with the layers 21, 23, 25 thereon. This canbe seen in FIG. 1 e . Since the semiconductor substrate 2 is n-doped inthe exemplary embodiment shown, the frontside doping layer 5 is alson-doped, preferably doped with phosphorus.

The frontside intrinsic layer 4 can be deposited separately from thefrontside doping layer 5 in different layer deposition reactors.However, it is particularly advantageous if, as has been done in theexemplary embodiment shown, the frontside doping layer 5 is depositeddirectly after the frontside intrinsic layer 4 in one and the same layerdeposition reactor without intermediate substrate handling. In thiscase, formation of air oxide between the frontside intrinsic layer 4 andthe frontside doping layer 5 is avoided.

In the case of the substrate handling required after this layerdeposition or these layer depositions, during which a substratetransport to the next layer deposition reactor takes place and thesubstrate is turned again, the layer structure produced and shownschematically in FIG. 1 e again reaches the atmosphere, which in turncauses air oxide layers 27, 28 on both sides of the layer structuregrow, which is shown in FIG. 1 f . The air oxide layers 27, 28 in theexemplary embodiment are SiO₂ layers having a layer thickness between0.2 and 3.0 nm.

After a further substrate handling, a backside doping layer 6 isproduced from an amorphous semiconductor material having a doping of asecond conductivity type, which is opposite to the first conductivitytype, on the back side of the layer arrangement shown in FIG. 1 f . Thisis shown in FIG. 1 g . In the exemplary embodiment shown, the backsidedoping layer 6 is a p-doped, amorphous silicon layer. Specifically, thep-type doping used in the example is a boron-type doping, but can be adifferent doping in other exemplary embodiments of the invention. Thebackside doping layer 6 forms the electrical contacting providedthereon, which is described below, and forms the emitter of the backsideemitter solar cell structure 1 to be formed having a heterojunction.

The layer structure from FIG. 1 g is subsequently transported to atleast one further layer deposition reactor, the layer structure beingagain exposed to atmospheric conditions during the transport.Approximately 0.2 to 3.0 nm thin air oxide layers 29, 30 are againformed on the front side and the back side of the layer structure, whichcan be seen in FIG. 1 h.

Thereafter, as is shown schematically in FIG. 1 i , electricallyconductive, transparent frontside and backside conduction layers 7, 8are produced on the front side and the back side of the layer structurefrom FIG. 1 h . The electrically conductive, transparent frontside andbackside conduction layers 7, 8 preferably consist of electricallyconductive, transparent oxide (TCO). In the exemplary embodiment shown,the electrically conductive, transparent frontside and backsideconduction layers 7, 8 are indium tin oxide layers (ITO layers).

In the exemplary embodiment shown, the electrically conductive,transparent backside conduction layer 8 is deposited on the at least onebackside doping layer 6 at a distance from the side edge 50 of thesemiconductor substrate 2. The backside doping layer 6 can be deposited,for example, via a mask. As a result, an edge region 51 on the back sideof the backside emitter solar cell structure 1 having a heterojunctionfrom the electrically conductive, transparent backside conductor layer 8remains uncoated. Due to the structured deposition, there is noelectrical contact between the electrically conductive, transparentbackside conduction layer 8 and the frontside conduction layer 7, noteven during the deposition of the electrically conductive, transparentbackside conduction layer 8.

Finally, frontside and backside contacts 9, 10 are produced on theelectrically conductive, transparent frontside and backside conductionlayers 7, 8, respectively. In the exemplary embodiment shown, thefrontside and backside contacts 9, 10 are made of silver and areprovided in finger shape on the front side and back side of the solarcells. However, they can also be formed from another, electricallyconductive material and/or applied in a different form.

As can be seen from the above statements, with each substrate transportair oxide layers 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 arise, whichform barriers between the semiconductor substrate 2 and the intrinsiclayers 3, 4 deposited thereon, between the backside intrinsic layer 4and the backside doping layer 6 as well as between the frontside andbackside doping layers 5, 6 and the respectively frontside and backsideconduction layers 7, 8 deposited thereon. These barriers hinder theconductor carrier transport and thus deteriorate the solar cellproperties of the backside emitter solar cell structure 1 to be formedhaving a heterojunction. As described above, by depositing the frontsidedoping layer 5 directly after the frontside intrinsic layer 4 in thesame layer deposition reactor, such a barrier formation between thefrontside intrinsic layer 4 and the frontside doping layer 5 could beavoided.

Furthermore, the process step sequence according to the invention, inwhich the boron-doped backside doping layer 6 is deposited as the lastof the amorphous semiconductor layers, limits the outdiffusion of boron,which has a higher diffusion coefficient than the phosphorus containedin the frontside doping layer 5, from the backside doping layer 6 to aminimum. This also advantageously influences the solar cell propertiesof the backside emitter solar cell structure 1 to be formed having aheterojunction.

As can be seen schematically in FIG. 2 , the procedure according to theinvention also has further advantageous effects. FIG. 2 schematicallyshows an intermediate product of the backside emitter solar cellstructure 1 according to the invention having a heterojunction from FIG.1 i . While in FIGS. 1 a to 1 i the layer sequences forming at the solarcell edge have been omitted for the sake of clarity, this layer sequenceis shown in FIG. 2 after the amorphous semiconductor layers 3, 4, 5 and6 have been deposited and before the formation of the further layers 7,8, 9, 10 particularly large.

Starting from the n-doped semiconductor substrate 2 in the illustratedembodiment, a n-i-i-n⁺-p layer sequence results at the edge of the solarcell. In contrast, in the prior art, the conventional process sequenceresults in an n-i-n⁺-i-p layer sequence. The double intrinsic layer 3, 4on the edge or on the side edge of the semiconductor substrate 2 seemsto protect the formed structure particularly against the formation ofshunt resistances and leakage currents at the edge of the solar cell.

FIGS. 3 and 4 schematically show partial areas of possible systemconcepts or devices 30, 40 for the production of backside emitter solarcell structures 1 having a heterojunction, as described above. Thedevice 30, which is shown schematically in regions in FIG. 3 , and thedevice 40, which is shown in regions in FIG. 4 , each have three layerdeposition strands 31, 32 and 42, 33 for the formation of the amorphoussemiconductor layers 3, 4, 5, 6.

In a first layer deposition strand 31, at least one layer depositionreactor 36 is provided for producing the at least one backside intrinsiclayer 3 on the back side of the semiconductor substrate 2.

In a second layer deposition strand 32 or 42, there is at least onelayer deposition reactor 39, 41; 44 for producing the at least onefrontside intrinsic layer 4 on the front side of the semiconductorsubstrate 2 and for producing the at least one frontside doping layer 5on the at least one frontside intrinsic layer 4. In the device 40, thesecond layer deposition strand 42 has only a single frontside layerdeposition reactor 44 for producing the at least one frontside intrinsiclayer 4 on the front side of the semiconductor substrate 2 and the atleast one frontside doping layer 5 on the at least one frontsideintrinsic layer 4.

In a third layer deposition strand 33, at least one layer depositionreactor 43 is provided for producing the at least one backside dopinglayer 6 on the at least one backside intrinsic layer 3.

A substrate transport and turning system 37 is provided in each casebetween the first layer deposition strand 31 and the second layerdeposition strand 32 or 42 and between the second layer depositionstrand 32 or 42 and the third layer deposition strand 33. In the devices30, 40, only a single substrate transport and turning system 37 isprovided, which is located in front of the frontside layer depositionreactor(s) 39, 41 and 44, respectively.

A lock device 45 is provided between and in front of the individuallayer deposition reactors.

A loading and unloading device 35 is provided at the beginning of eachlayer deposition strand 31, 32 and 42, 33.

The invention claimed is:
 1. A method for producing a backside emittersolar cell structure having a heterojunction, the method comprising thefollowing steps in the following order: providing a crystallinesemiconductor substrate having a doping of a first conductivity type toform an absorber of the backside emitter solar cell structure; producingon a back side of the semiconductor substrate at least one backsideintrinsic layer made of an intrinsic, amorphous semiconductor material;producing on a front side of the semiconductor substrate at least onefrontside intrinsic layer from an intrinsic, amorphous semiconductormaterial; producing on the at least one frontside intrinsic layer atleast one frontside doping layer from an amorphous semiconductormaterial having a doping of the first conductivity type which is higherthan the doping of the semiconductor substrate; forming an emitter ofthe backside emitter solar cell structure having heterojunction on theat least one backside intrinsic layer, by producing at least onebackside doping layer from an amorphous semiconductor material with adoping of a second conductivity type opposite to the first conductivitytype; producing on the at least one frontside doping layer at least oneelectrically conductive, transparent frontside conduction layer;producing on the at least one backside doping layer at least oneelectrically conductive, transparent backside conduction layer;producing a frontside contact on the at least one electricallyconductive, transparent frontside conduction layer; and producing abackside contact on the at least one electrically conductive,transparent backside conduction layer; wherein the at least oneelectrically conductive, transparent backside conduction layer isdeposited on the at least one backside doping layer at a spacingdistance from a side edge of the semiconductor substrate, so that anedge region on the back side of the backside emitter solar cellstructure having heterojunction is not coated with the electricallyconductive, transparent backside conduction layer and in all processsteps for forming the electrically conductive, transparent backsideconduction layer, there is no electrical contact between theelectrically conductive, transparent backside conduction layer and thefrontside conduction layer.
 2. The method according to claim 1, whichcomprises providing an n-doped semiconductor substrate as thesemiconductor substrate, producing the frontside doping layer with anamorphous semiconductor material doped with phosphorus, and producingthe backside doping layer with an amorphous semiconductor material dopedwith boron.
 3. The method according to claim 1, which comprisesproducing the at least one frontside intrinsic layer on the front sideof the semiconductor substrate and producing the at least one frontsidedoping layer on the at least one frontside intrinsic layer in processestaking place one after another in one and the same layer depositionreactor.
 4. A backside emitter solar cell structure having aheterojunction, the solar cell structure comprising: an absorber made ofa crystalline semiconductor substrate having a doping of a firstconductivity type; at least one frontside intrinsic layer formed on afront side of said absorber and made of an intrinsic, amorphoussemiconductor material; at least one backside intrinsic layer formed ona back side of said absorber and made of an intrinsic, amorphoussemiconductor material; at least one frontside doping layer formed onsaid at least one frontside intrinsic layer made of an amorphoussemiconductor material having a doping of the first conductivity typewhich is higher than the doping of said absorber; an emitter of at leastone backside doping layer formed on said at least one backside intrinsiclayer and made of an amorphous semiconductor material having a doping ofa second conductivity type opposite the first conductivity type; atleast one electrically conductive, transparent frontside conductionlayer formed on said at least one frontside doping layer; at least oneelectrically conductive, transparent backside conduction layer formed onsaid at least one backside doping layer; a frontside contact formed onsaid at least one electrically conductive, transparent frontsideconduction layer; and a backside contact formed on said at least oneelectrically conductive, transparent backside conduction layer; whereinat one side edge of the backside emitter solar cell structure, on anedge region of the semiconductor substrate, a layer sequence havinglayers in the following sequence are present from inside to outside:said at least one backside intrinsic layer; said at least one frontsideintrinsic layer on said at least one backside intrinsic layer; said atleast one frontside doping layer on said at least one frontsideintrinsic layer; and said at least one backside doping layer on said atleast one frontside doping layer; and wherein said at least oneelectrically conductive, transparent backside conduction layer isdeposited on the at least one backside doping layer at a distance fromsaid side edge of said semiconductor substrate, so that an edge area ona back side of said backside emitter solar cell structure is not coatedwith said electrically conductive, transparent backside conduction layerand there is no electrical contact between said electrically conductive,transparent backside conduction layer and said frontside conductionlayer.
 5. The backside emitter solar cell structure according to claim4, wherein said semiconductor substrate is an n-doped semiconductorsubstrate, said frontside doping layer is doped with phosphorus, andsaid backside doping layer is doped with boron.